(1) Field of the Invention
This invention relates to a hydrogen-absorbing alloy electrode used as a negative electrode of a metal-hydrogen alkaline storage cell.
(2) Description of the Prior Art
Lead cells and nickel-cadmium cells have long been in wide use as storage cells. In recent years, however, a nickel-hydrogen alkaline storage cell has been drawing attention because it is lighter in weight and has larger capacity than these cells. The nickel-hydrogen alkaline storage cell comprises a negative electrode made from a hydrogen-absorbing alloy capable of reversibly absorbing and desorbing hydrogen, and a positive electrode made from metallic oxide such as nickel hydroxide.
Such a hydrogen-absorbing alloy used for a negative electrode is required to be able to reversibly absorb and desorb hydrogen around room temperature. Developed to meet the requirement are Mm-Ni system alloys (disclosed in Japanese Laid-Open Patent Application No. 60-89066), Ti system alloys (disclosed in Japanese Patent Publication No. 59-50744) and others.
The Mm-Ni system alloys are already put to practical use, but new alloys of Ti system or Zr system are proposed to realize larger capacity, such as ones in Japanese Laid-Open Patent Applications 59-78908, 60-241652, 63-284758, 64-48370 and U.S. Pat. No. 4,923,770. Drawing special attention among them is a Ti-Mo alloy having TiMo-based crystalline cubic-structure, because it has the advantage of reversibly absorbing and desorbing larger amounts of hydrogen in a solid-gas reaction than rate-earth-Ni system alloys.
However, the above-mentioned new alloys of Ti system or Zr system having larger capacity than the Mm-Ni system alloys have a disadvantage of low productivity because it is difficult to crush the alloys due to their hardness and ductility.
Also, cells employing the Ti system alloy have the same disadvantage of low productivity because it takes a long time to carry out an activation treatment.